Nanomechanical properties of sub-10 nm carbon film overcoats using the nanoindentation technique
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James D. Kiely and Yiao-Tee Hsia Seagate Research, Pittsburgh, Pennsylvania 15222 (Received 23 May 2006; accepted 13 September 2006)
The hardness and elastic modulus of ultra thin amorphous carbon overcoat (COC) films were measured using a recently developed sub-nm nanoindentation system. The carbon overcoat film thickness was varied to be 2.5 nm, 5 nm, and 10 nm on a glass substrate with a 2 nm titanium interlayer. A very sharp indenting tip, which was a cube corner tip with a radius of 44 nm, was used for the experiments. It was found that the mechanical properties of sub-10 nm film thicknesses can be reliably measured using the sub-nm indentation system and a sharp indenting tip. As the thickness of the carbon overcoat increased, so too did the surface roughness. For all three film thickness samples, the trends of hardness and elastic modulus values with the contact depth are very similar. When the contact depth is smaller than the film thickness, the measured values of hardness and elastic modulus are higher than those of the glass substrate, and gradually decrease and then approach the values of glass substrate. When the contact depth is larger than the film thickness, the measured values approximate those of the glass substrate. The thinner film shows higher values of hardness and elastic modulus near the surface, which indicates that mechanical properties do change with film thickness and that measurements made on thicker films and extrapolated to thinner films may lead to incorrect conclusions. I. INTRODUCTION
Diamondlike-carbon (DLC) films form a critical protective layer for various industrial applications such as magnetic storage, semiconductor packaging, and medical implants. As the applications become smaller and more sophisticated, there is a concurrent demand to have a thinner film on the substrate. In the case of the magnetic storage industry because the physical spacing between the head and disk is critical to the storage density, ultra thin layers of diamondlike-carbon, typically referred to as the carbon overcoat (COC) are required. It is projected that a COC layer of a few nanometers thick and a subnanometer roughness are needed for storage of 1 Tbit/in2 areal density.1,2 Under these requirements of the magnetic storage industry, and because the lower flying height with thinner COC film can give critical concerns for the tribological and reliability performance of the head disk interface (HDI), the characterization of mechanical properties such as hardness and elastic modulus is of critical importance for the robust design of
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0007 J. Mater. Res., Vol. 22, No. 1, Jan 2007
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such products. For these reasons, it is necessary to make accurate measurements of the mechanical properties of ultra thin films. With high resolution loading/unloading displacement control and force sensors, instrumented nanoindentation systems have been widely used to evalua
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